A partition is provided at the almost center of a parallel sheet feed tray in a main-scanning direction, and recording paper sheets such as postcards are mounted in two rows in parallel in the main-scanning direction. By bringing upper surfaces of the recording paper sheets into contact with a pick roller, the recording paper sheets are picked one by one per row and fed toward an inside of a housing. While the recording paper sheets are conveyed in a sub-scanning direction with being arranged in parallel in the main-scanning direction, ink drops are discharged to both the recording paper sheets with reciprocation of a carriage with the ink cartridges in the main-scanning direction. Images are formed on the two recording paper sheets simultaneously, thereby shortening time necessary for printing a lot of recording paper sheets.